1. Field of the Invention
The invention relates to a high-power radiator, especially for ultraviolet light, having a discharge space which is filled with a filling gas which emits radiation under discharge conditions, formed by the internal space of a cooled hollow body consisting of a material which is transparent to the radiation generated, with dielectric tubes which are spaced from the inner walls of the hollow body and which are provided with cooling channels and into which inner electrodes are embedded or inserted, with a high-tension source to feed the discharge.
Accordingly, the invention refers to a state of the art as is evident, for example, from the EP application bearing the publication number 0,363,832.
2. Discussion of Background
The industrial application of photochemical processes is greatly dependent upon the availability of suitable UV sources. The conventional UV radiators give low to medium UV intensities at a few discrete wavelengths, such as, for example, the low-pressure mercury lamps operating at 185 nm and especially at 254 nm. Really high UV power levels are achieved only from high-pressure lamps (Xe, Hg), which then however distribute their radiation over a greater wavelength range. The new excimer lasers made available certain new wavelengths for photochemical basic experiments. However, at the present time they are only in exceptional cases suitable for an industrial process, for reasons of cost.
A novel excimer radiator is described in the initially mentioned EP patent application, or also in the conference publication "Novel UV and VUV Excimer Radiators" by U. Kogelschatz and B. Eliasson, distributed at the 10th lecture meeting of the German Chemists Association, Photochemistry Technical Group, in Wurzburg (FRG) on Nov. 18-20, 1987. This novel type of radiator is based on the principle that it is possible to generate excimer radiation even in silent electrical discharges, a type of discharge which is employed on an industrial scale in the production of ozone. In the current filaments of this discharge, which are present only for a short time (a few nanoseconds) inert gas atoms are excited by electron collision, which atoms react further to form excited molecular complexes (excimers). These excimers have a life of only a few nanoseconds, and on breaking up give off their binding energy in the form of radiation, the wavelength range of which may be in the UVA, UVB, UVC and VUV or also in the visible spectral range, depending upon the composition of the filling gas.
In very recent times the search for such high-power radiators has intensified, since the particular properties of the radiator have opened up many new areas of application in chemical and physical process technology, in the graphics industry, for coatings etc.
In addition to an optimal design of the radiator with regard to dielectric material, slit width, pressure, temperature and composition of the gas employed, the effective cooling of the radiator is also of decisive importance with regard to its commercial application. In the case of the known radiators, the outer electrode which is at earth potential is regularly cooled. An optional feature is also a cooling of the inner electrode (which is at high-tension potential), in this connection it merely being stated that a liquid or gaseous coolant is passed through the hollow inner electrode. On account of the potential conditions, when liquid cooling is employed it is necessary to use a coolant which exhibits a very low conductance, e.g. fully demineralized water, or oil. In addition, the cooling of the inner electrode must take place in a closed circuit, on economic grounds.